Municipality Brežice, which is part of the Posavska statistical region, measures 268 km2; this ranks it 14th among Slovene municipalities.
Statistical data for 2021 reveal the following:
In the middle of 2021 about 24,350 people (about 12,200 men and 12,140 women) were living in the municipality, which ranks Brežice 13th among Slovene municipalities. The population density was 91 people per square kilometre, which was lower than the national average of 104 people per square kilometre.
The number of live births was lower than the number of deaths, which means that natural increase per 1,000 population in the municipality was negative. It was -3.9 (in Slovenia -2.0). The number of people who moved from the municipality was lower than the number of people who moved into the municipality, so net migration per 1,000 population in the municipality was positive. It was 2.3. The sum of natural increase and net migration per 1,000 population in the municipality was positive. It was 1.4 (in Slovenia -0.9).
The mean age of people in Brežice was 45.4 years, which was lower than the national average (43.8).
As in most Slovene municipalities, in Brežice the number of old people was higher than the number of young people: there were 168 people, aged 65 or more, per 100 people aged 0–14. This ratio shows that the value of the ageing index was higher than the national average of 139. It also shows that the mean age of people in Brežice is growing more rapidly than in Slovenia as a whole. Data by sex show that the ageing index for women was in all municipalities except in five (Črna na Koroškem, Dobrovnik/Dobronak, Jezersko, Loški Potok in Mislinja) higher than the ageing index for men. In Brežice – as in most Slovene municipalities – more women were 65+ years old than 14 or less; for men the situation was the same.
Brežice had 9 kindergartens, which were attended by 886 children. Of all children in the municipality aged 1–5, 80% were included in kindergartens, which was less than the national average of 81%. In the school year 2021/22 elementary schools in Brežice were attended by about 2,060 pupils, while various upper secondary schools were attended by about 810 pupils. There were 31 students and 7 graduates per 1,000 people in the municipality; in Slovenia the averages were 39 per 1,000 and 8 per 1,000, respectively.
Among people aged 15–64 (i.e. working age population) about 67% were persons in employment (i.e. persons in paid employment or self-employed persons), which is the same as the national average.
In Brežice, average monthly gross earnings per person employed by legal persons were about 8% lower than the annual average of monthly earnings for Slovenia; net earnings were about 7% lower.
Among 1,000 inhabitants in the municipality, 586 had a passenger car. The car was on average 11 years old.
In 2021, 304 kg of municipal waste per person was collected in Brežice, which is 61 kg less than on average in Slovenia.